A lower track of a general crawler type excavator shown in FIG. 1 includes:                a plurality of track shoes 1 each configured to form a ground plane of a crawler to allow an orbital motion of the track shoes to be performed by a drive wheel (i.e., referring to a sprocket) connected to a travel motor (not shown);        a pair of opposed track links 3 and 4 each mounted on the track shoe 1 by means of a bolt or the like and including a plurality of link segments consecutively connected to each other by a plurality of track pins to allow the orbital motion of the track shoes to be performed by the drive wheel;        a plurality of bushings 5 engaged into associated ones of engagement holes 3a and 4a formed to confront each other in the track links 3 and 4 in such a manner that the bushings are spaced apart from each other at equal distances, and configured to surroundingly support the track pins 2.        
Since such a crawler type excavator causes damage to an asphalt or concrete surface when it travels on the asphalt or concrete surface, a rubber pad is mounted on a track shoe by a bolt or the like to prevent damage of a road surface due to its travel.
A means for mounting a rubber pad to a track shoe of a crawler type excavator in accordance with the prior art as shown in FIG. 2(a) includes a plurality of fastening members 7 (for example, four bolts are used) protrudingly formed on the underside of the rubber pad 6, a plurality of fastening holes 1a penetratingly formed on the track shoe 1 to correspond to the fastening members 7, and a plurality of fastening nut 8 fastened to the fastening members 7 engaged into the fastening holes 1a. 
As described above, the lower track of the conventional crawler type excavator in accordance with one embodiment of the prior art entails a problem in that the fastening holes 1a are required to be separately drilled on the track shoe 1 in order to mount the rubber pad 6 to the track shoe 1, leading to an increase in the manufacturing cost and a degradation of the strength of the track shoe 1 due to the drilled fastening holes 1a. 
A means for mounting a rubber pad to a track shoe of a crawler type excavator in accordance with the prior art as shown in FIG. 2(b) includes a pair of hooks 9 formed on one side of the underside of a rubber pad 6 so as to allow a track shoe 1 to be fixedly seated thereon, and a pair of fastening members 10 (for example, two bolts are used) engaged into screw holes (not shown) formed on the other side of the underside of the rubber pad 6 via through-holes 1a formed on one side of the track shoe 1 seated on the hooks 9.
As described above, the lower track of the conventional crawler type excavator in accordance with one embodiment of the prior art entails a problem in that the fastening holes 1a are required to be separately drilled on the track shoe 1 in order to mount the rubber pad 6 to the track shoe 1, leading to an increase in the manufacturing cost and a degradation of the strength of the track shoe 1 due to the drilled fastening holes 1a. 
A means for mounting a rubber pad to a track shoe of a crawler type excavator in accordance with the prior art as shown in FIG. 2(c) includes a pair of hooks 9 formed on one side of the underside of a rubber pad 6 so as to allow a track shoe 1 to be fixedly seated thereon, a bottom plate hook 11 mounted on one side of the rubber pad 6 so as to support the other side of the track shoe supported at one side thereof by the hooks 9, and a pair of fastening members 10 engaged into screw holes 6a formed on a side of the rubber pad 6 via through-holes 1a formed on the bottom plate hook 11.
As described above, the lower track of the conventional crawler type excavator in accordance with one embodiment of the prior art entails a problem in that the heads of the fastening members 10 are protrudingly exposed to the outside in order to mount the rubber pad 6 to the track shoe 1, the fastening members 10 may be damaged due to a shock applied thereto from the outside, leading to an escape of the rubber pad 6 from the track shoe 1.